Water electrolysis system

ABSTRACT

A water electrolysis system includes a water electrolysis apparatus for electrolyzing pure water supplied from a pure water supply apparatus for manufacturing high-pressure hydrogen. The water electrolysis apparatus has a pipe serving as a hydrogen outlet to which a gas-liquid separator, a cooler, and a water adsorption apparatus are successively connected in this order along the direction in which hydrogen is discharged from the water electrolysis apparatus. A first back-pressure valve is connected between the cooler and the water adsorption apparatus, and a second back-pressure valve is connected downstream of the water adsorption apparatus.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Patent Application No. 2009-045708 filed on Feb. 27, 2009, in the Japan Patent Office, of which the contents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water electrolysis system having a water electrolysis apparatus for electrolyzing water with an electric current supplied from a DC power supply to generate hydrogen and oxygen, and a water adsorbing apparatus for adsorbing water in the hydrogen generated by the water electrolysis apparatus, the water adsorbing apparatus being connected downstream of a hydrogen discharge port of the water electrolysis apparatus which discharges the hydrogen.

2. Description of the Related Art

Solid polymer electrolyte fuel cells generate DC electric energy when anodes thereof are supplied with a fuel gas, i.e., a gas mainly composed of hydrogen, e.g., a hydrogen gas, and cathodes thereof are supplied with an oxygen-containing gas, a gas mainly composed of oxygen, e.g., air.

Generally, water electrolysis apparatus are used to generate a hydrogen gas for use as a fuel gas for such solid polymer electrolyte fuel cells. The water electrolysis apparatus employ a solid polymer electrolyte membrane (ion exchange membrane) for decomposing water to generate hydrogen (and oxygen). Electrode catalytic layers are disposed on the respective sides of the solid polymer electrolyte membrane, making up a membrane electrode assembly. Electric feeders are disposed on the respective sides of the membrane electrode assembly, making up a unit. The unit is essentially similar in structure to the fuel cells described above.

A plurality of such units are stacked, and a voltage is applied across the stack while water is supplied to the electric feeders on the anode side. On the anodes of the membrane electrode assemblies, the water is decomposed to produce hydrogen ions (protons). The hydrogen ions move through the solid polymer electrolyte membranes to the cathodes, where the hydrogen ions combine with electrons to generate hydrogen. On the anodes, oxygen generated together with hydrogen is discharged with excess water from the units.

Such a water electrolysis system generates hydrogen under a high pressure of several tens MPa. Japanese Laid-Open Patent Publication No. 2007-100204 discloses a method of and an apparatus for manufacturing high-pressure hydrogen. As shown in FIG. 7 of the accompanying drawings, the disclosed apparatus for manufacturing high-pressure hydrogen comprises a high-pressure oxygen vessel 1, a differential pressure regulator 2, a high-pressure hydrogen vessel 3, an electrolytic cell 4, a water adsorption tube 5, a back-pressure valve 6, and a deoxidization tube 7.

Pure water contained in the high-pressure oxygen vessel 1 is delivered to an anode side of the electrolytic cell 4 by a circulation pump 8. The pure water delivered to the electrolytic cell 4 is electrolyzed when the electrolytic cell 4 is energized by a power supply 9. Oxygen generated from the pure water by the electrolytic cell 4 is delivered, together with returning pure water from the circulation pump 8, to the high-pressure oxygen vessel 1.

Hydrogen generated at the cathode of the electrolytic cell 4 is discharged, together with permeated water, into the high-pressure hydrogen vessel 3. At this time, the differential pressure regulator 2 equalizes the pressure in the high-pressure oxygen vessel 1 and the pressure in the high-pressure hydrogen vessel 3 to each other.

The hydrogen stored in the high-pressure hydrogen vessel 3 is delivered to the deoxidization tube 7, which removes oxygen contained in the hydrogen. The hydrogen is then delivered from the deoxidization tube 7 through the back-pressure valve 6 to the water adsorption tube 5, which removes water from the hydrogen, thereby finalizing the hydrogen as a product.

According to Japanese Laid-Open Patent Publication No. 2007-100204, the high-pressure hydrogen stored in the high-pressure hydrogen vessel 3 may be abruptly introduced through the back-pressure valve 6 into the water adsorption tube 5. When the high-pressure hydrogen is abruptly introduced into the water adsorption tube 5, the water adsorption tube 5 may not be able to adsorb water well from the high-pressure hydrogen because the high-pressure hydrogen flows at an excessively high speed. In order for the water adsorption tube 5 to have a high water adsorbing capability, it needs to have a large amount of adsorbent. However, the water adsorption tube 5 with a large amount of adsorbent will become considerably large in size and is not economical.

In addition, if the pressure difference between the water adsorption tube 5 and the hydrogen tank of a fuel cell vehicle is large, then the water adsorption tube 5 is likely to be released from the pressure. When the water adsorption tube 5 is released from the pressure, the adsorbed water tends to be released from the adsorbent in the water adsorption tube 5 and introduced into the hydrogen tank.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a water electrolysis system of simple structure which is capable of reliably preventing water contained in hydrogen from passing through a water adsorption apparatus and hence of efficiently supplying desired dry hydrogen.

According to the present invention, a water electrolysis system includes a water electrolysis apparatus for electrolyzing water with an electric current supplied from a DC power supply to generate hydrogen and oxygen, and a water adsorption apparatus connected downstream of and connected to a hydrogen outlet of the water electrolysis apparatus, for adsorbing water contained in the hydrogen discharged from the hydrogen outlet.

The water electrolysis system has a first pressure regulating valve connected between the hydrogen outlet and the water adsorption apparatus, and a second pressure regulating valve connected downstream of the water adsorption apparatus.

According to the present invention, since the second pressure regulating valve is connected downstream of the water adsorption apparatus, the pressure acting in the water adsorbing apparatus can be kept at a preset pressure. Therefore, hydrogen containing water does not quickly flow through the water adsorbing apparatus, which is thus able to reliably adsorb the water contained in the hydrogen. Further, as the pressure acting in the water adsorbing apparatus is kept at a preset pressure, the adsorbed water in the water adsorbing apparatus is prevented from being released therefrom and flowing downstream of the water adsorbing apparatus.

Further, the first pressure regulating valve is connected between the hydrogen outlet and the water adsorbing apparatus. As a result, the water adsorbing apparatus can be isolated from the region upstream thereof. Thus, the water adsorbing apparatus, for example, can be cleaned easily and efficiently. Therefore, the water electrolysis system is of a relatively simple structure for reliably preventing water contained in the hydrogen from passing through the water adsorbing apparatus, and also for efficiently supplying desired dry hydrogen.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a water electrolysis system according to an embodiment of the present invention;

FIG. 2 is a diagram illustrative of the manner in which the pressures on first and second back-pressure valves of the water electrolysis system change with time;

FIG. 3 is a schematic diagram illustrative of a pressure increase up to the first back-pressure valve;

FIG. 4 is a schematic diagram illustrative of a pressure increase up to the second back-pressure valve;

FIG. 5 is a diagram illustrative of the manner in which the pressures on the second back-pressure valve change with time when the water electrolysis system resumes its operation;

FIG. 6 is a diagram illustrative of the manner in which the pressures on the first and second back-pressure valves change with time when a water adsorption apparatus is released from the pressure and the water electrolysis system resumes its operation; and

FIG. 7 is a schematic diagram of an apparatus for manufacturing high-pressure hydrogen disclosed in Japanese Laid-Open Patent Publication No. 2007-100204.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a water electrolysis system 10 according to an embodiment of the present invention comprises a water electrolysis apparatus 14 for being supplied with pure water that has been generated from city water from a pure water supply apparatus 12 and electrolyzing the pure water to produce high-pressure hydrogen (whose pressure is higher than a normal pressure), a gas-liquid separator 18 for removing water contained in the high-pressure hydrogen which is delivered from the water electrolysis apparatus 14 into a hydrogen outlet passage 16, a cooler 20 for cooling the hydrogen discharged from the gas-liquid separator 18, a water adsorbing apparatus 22 for adsorbing away water contained in the cooled hydrogen discharged from the cooler 20, and a hydrogen tank 26 for storing the hydrogen (dry hydrogen) delivered from the water adsorbing apparatus 22 into a dry hydrogen supply passage 24. The hydrogen tank 26 is optional, and may be added when necessary or may be dispensed with.

The water electrolysis apparatus 14 comprises a stack of water decomposition cells 28 and a pair of end plates 30 a, 30 b disposed respectively on the opposite ends of the stack of water decomposition cells 28. An electrolytic power supply 32 in the form of a DC power supply is connected across the water electrolysis apparatus 14. The water electrolysis apparatus 14 has an anode connected to the positive terminal of the electrolytic power supply 32 and a cathode connected to the negative terminal of the electrolytic power supply 32.

A pipe 34 a is connected to the end plate 30 a, and pipes 34 b, 34 c are connected to the end plate 30 b. The pure water from the pure water supply apparatus 12 is circulated through a circulation passage 35 to the pipes 34 a, 34 b. The pipe 34 c, which serves as a hydrogen outlet, is connected by the hydrogen outlet passage 16 to the gas-liquid separator 18.

The hydrogen outlet passage 16 includes a first back-pressure valve (first pressure regulating valve) 36 connected between the pipe 34 c and the water adsorbing apparatus 22, or more specifically between the cooler 20 and the water adsorbing apparatus 22, and a bleeder passage 38 branched from the hydrogen outlet passage 16 between the first back-pressure valve 36 and the water adsorbing apparatus 22. The bleeder passage 38 has an on-off valve, e.g., a solenoid-operated valve 40. The first back-pressure valve 36 has a first preset pressure.

The water adsorbing apparatus 22 includes an adsorption tower (not shown) filled with a water adsorbent (not shown) for physically adsorbing a water vapor (water) contained in hydrogen, the water adsorbent being regenerated when it discharges adsorbed water. The dry hydrogen supply passage 24 is connected downstream of the water adsorbing apparatus 22, i.e., is connected to the outlet port of the water adsorbing apparatus 22, through a second back-pressure valve (second pressure regulating valve) 42. The second back-pressure valve 42 has a second preset pressure which is equal to or higher than the first preset pressure of the first back-pressure valve 36 (see FIG. 2). The first back-pressure valve 36 and the second back-pressure valve 42 may be replaced with various valves such as solenoid-operated valves.

The hydrogen tank 26 is connected to the dry hydrogen supply passage 24. A hydrogen supply passage 46 is connected to the hydrogen tank 26 through an on-off valve 48. The hydrogen supply passage 46 can be connected directly or via a reservoir tank, not shown, to the fuel tank of a fuel cell vehicle 50.

Operation of the water electrolysis system 10 will be described below.

When the water electrolysis system 10 starts to operate, the water electrolysis apparatus 14 is supplied with pure water that has been generated from city water from the pure water supply apparatus 12. The water electrolysis apparatus 14 electrolyzes the pure water to produce hydrogen when it is energized by the electrolytic power supply 32.

The hydrogen generated by the water electrolysis apparatus 14 is delivered through the hydrogen outlet passage 16 to the gas-liquid separator 18. In the gas-liquid separator 18, a water vapor contained in the hydrogen is separated from the hydrogen. The hydrogen is then delivered to the cooler 20 in which it is cooled. Therefore, the water in the hydrogen is condensed and separated as condensed water from the hydrogen.

The first back-pressure valve 36 is connected downstream of the cooler 20. As shown in FIG. 2, the cooler 20 can pressurized the hydrogen until the first preset pressure of the first back-pressure valve 36 is reached, i.e., until time T1 (see FIG. 3). Consequently, the water in the hydrogen is reliably condensed and separated as condensed water from the hydrogen.

When the hydrogen pressure in a hydrogen system that ranges from the water electrolysis apparatus 14 to the cooler 20 increases to the first preset pressure of the first back-pressure valve 36, the first back-pressure valve 36 is opened. The high-pressure hydrogen, i.e., the hydrogen whose pressure has risen to the first preset pressure, flows through the first back-pressure valve 36 into the water adsorbing apparatus 22. The water adsorbing apparatus 22 then adsorbs a water vapor contained in the supplied hydrogen, producing dry hydrogen.

The second back-pressure valve 42 is connected downstream of the water adsorbing apparatus 22. Therefore, the dry hydrogen is held under pressure within the water adsorbing apparatus 22 (see FIG. 4) until the pressure of the hydrogen in the water adsorbing apparatus 22 reaches the second preset pressure of the second back-pressure valve 42, i.e., from time T1 to time T2 (see FIG. 2). When the pressure of the hydrogen in the water adsorbing apparatus 22 reaches the second preset pressure, the second back-pressure valve 42 is opened, introducing the dry hydrogen from the water adsorbing apparatus 22 into the dry hydrogen supply passage 24.

The dry hydrogen delivered to the dry hydrogen supply passage 24 is stored in the hydrogen tank 26. When necessary, the dry hydrogen stored in the hydrogen tank 26 is sent through the hydrogen supply passage 46 to the fuel cell vehicle 50, filling the fuel tank thereof, by opening the on-off valve 48.

According to the present embodiment, the second back-pressure valve 42 is connected downstream of the water adsorbing apparatus 22. Therefore, the pressure acting in the water adsorbing apparatus 22 can be kept at a preset pressure, i.e., the second preset pressure. Specifically, the speed at which the hydrogen in the water adsorbing apparatus 22 flows is nil after the first back-pressure valve 36 disposed upstream of the water adsorbing apparatus 22 is opened until the second back-pressure valve 42 is opened, i.e., from time T1 to time T2 shown in FIG. 2.

Therefore, the hydrogen containing water which is introduced from the cooler 20 does not quickly flow through the water adsorbing apparatus 22, which is thus able to reliably adsorb the water contained in the hydrogen with the water adsorbent (not shown).

Since the pressure acting in the water adsorbing apparatus 22 is kept at a preset pressure, the adsorbed water in the water adsorbing apparatus 22 is prevented from being released from the water adsorbent and flowing downstream of the water adsorbing apparatus 22 into the hydrogen tank 26.

The first back-pressure valve 36 is connected between the water electrolysis apparatus 14 and the water adsorbing apparatus 22, or more specifically between the cooler 20 and the water adsorbing apparatus 22. As a result, the water adsorbing apparatus 22 can be isolated from the region upstream thereof, i.e., from the cooler 20, by the first back-pressure valve 36. Thus, the water adsorbing apparatus 22 can be cleaned easily and efficiently.

The water electrolysis system 10 is of a relatively simple structure for reliably preventing water contained in the hydrogen from passing through the water adsorbing apparatus 22, and also for efficiently supplying the desired dry hydrogen.

The water adsorbing apparatus 22 can be isolated from the water electrolysis apparatus 14 by the first back-pressure valve 36. When the water electrolysis system 10 is temporarily shut down, therefore, the interior of the water adsorbing apparatus 22 can be maintained under a desired pressure. When the water electrolysis system 10 subsequently resumes its operation at time T3 shown in FIG. 5, the time required to increase the pressure in the water adsorbing apparatus 22 is thus effectively shortened.

For releasing the water adsorbing apparatus 22 from the pressure when the water adsorbing apparatus 22 is to be cleaned, the water adsorbing apparatus 22 is shut down and the solenoid-operated valve 40 is opened, releasing the water adsorbing apparatus 22 from the pressure at time T4 shown in FIG. 6. When the water electrolysis system 10 subsequently resumes its operation at time T5, the pressure from the water electrolysis apparatus 14 to the water adsorbing apparatus 22 starts to increase at time T6 while the second back-pressure valve 42 is being closed. Therefore, water contained in the hydrogen does not quickly pass through the water adsorbing apparatus 22, but is reliably adsorbed by the water adsorbent (not shown) in the water adsorbing apparatus 22.

Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. 

1. A water electrolysis system comprising: a water electrolysis apparatus for electrolyzing water with an electric current supplied from a DC power supply to generate hydrogen and oxygen; a water adsorption apparatus disposed downstream of and connected to a hydrogen outlet of the water electrolysis apparatus, for adsorbing water contained in the hydrogen discharged from the hydrogen outlet; a first pressure regulating valve connected between the hydrogen outlet and the water adsorption apparatus; and a second pressure regulating valve connected downstream of the water adsorption apparatus.
 2. A water electrolysis system according to claim 1, wherein the second pressure regulating valve has a preset pressure which is higher than a preset pressure of the first pressure regulating valve.
 3. A water electrolysis system according to claim 1, further comprising a gas-liquid separator and a cooler, wherein the gas-liquid separator, the cooler, and the first pressure regulating valve are successively positioned in this order between the hydrogen outlet and the water adsorption apparatus, along a direction in which the hydrogen flows.
 4. A water electrolysis system according to claim 1, wherein each of the first pressure regulating valve and the second pressure regulating valve comprises a back-pressure valve.
 5. A water electrolysis system according to claim 1, wherein the water electrolysis apparatus discharges the hydrogen under a pressure higher than a normal pressure.
 6. A water electrolysis system according to claim 1, further comprising a bleeder passage having an on-off valve, the bleeder passage being connected between the first pressure regulating valve and the water adsorbing apparatus. 